Polymerization of alpha-betaunsaturated monomers



3,048,572 POLYMERIZATION F ALPHA-BETA- UNSATURATED MONOMERS Frank Joseph Welch, Charleston, W. Va., assignor to gnifin Carbide Corporation, a corporation of New or No Drawing. Filed Sept. 11, 1959, Ser. No. 839,279 9 Claims. (Cl. 260-885) The present invention relates to organic processes, and more particularly, to novel and improved processes for polymerizing alpha,beta-unsaturated monomers.

Alpha,beta-unsaturated monomers, such as. methyl methacrylate, ethyl acrylate, acrylonitrile and the like,

have heretofore been polymerized by many methods, among which, there may be mentioned anionic polymerizations involving the use as a catalyst of sodium naphthalene or potassium amide in liquid ammonia. In these conventional anionic polymerizations, the reactions are ordinarily carried out at low temperatures, e.g. between about 80 C. and 33 C., if relatively high molecular weight polymers are to be obtained. Thus, in such processes, the use of complex and costly equipment capable of producing and maintaining these low temperatures in the reaction system is unfortunately necessitated. Another disadvantage encountered therein lies in the reactivity of ammonia with esters such as the alkyl acrylates and methacrylates to form acrylamides and methacrylamides, respectively. As a consequence of this reactivity the polymeric materials obtained by the polymerization of alkyl acrylates or methacrylates contain numerous amide groups in the polymer chain.

These disadvantages can now be overcome through the practice of this invention which, in its broadest aspect, is directed to processes for polymerizing -alpha,beta-unsaturated monomers, as hereinafter described, in contact with a catalytic amount of an alkaline earth metal amide catalyst. The polymerization can be carried out as a bulk process, but preferably is carried out in the presence of an inert organic diluent which does not participate in or interfere with the reaction.

Performed in accordance with this invention, the polymerization of the alpha,beta-unsaturated monomers can be conducted efficiently at temperatures of up to about 150 C. or somewhat higher, thereby obviating the disadvantage of low temperature operation. Moreover, the polymeric products obtained in accordance with this invention are ordinarily solid products which possess a molecular weight appreciably in excess of that possessed by the polymeric products produced by the conventional anionic polymerizations hereinabove described.

By the term reduced viscosity, as used herein including the appended claims, is meant a value obtained by dividing the specific viscosity of a solution of the polymer by the concentration of the polymer in the solution, the concentration being measured in grams of polymer per 100 milliliters of solvent at a given temperature, and it is regarded as a measure of molecular weight. The specific viscosity is obtained by dividing the difference between the viscosity of the solution and the viscosity of the solvent by the viscosity of the solvent. Unless otherwise indicated, the reduced viscosity value is determined at a concentration of 0.2 gram of polymer per 100 milliliters of solvent, at a temperature of 30 C.

The alpha,beta-unsaturated monomers contemplated by this invention can be defined more clearly by representation in connection with the following general formula:

wherein A designates a member of the class consisting of atent C hydrogen and halogen atoms and the alkyl radicals containing from 1 to about 4 carbon atoms and preferably from 1 to about 2 carbon atoms, and B designates a member of the class consisting of the --CN,

1? O-OR I -NH and H --CNRQ radicals wherein R designates an alkyl radical containing from 1 to about 12 carbon atoms and preferably from 1 to about 4 carbon atoms. The alkyl radicals hereinabove described can also be substituted by groups which are inert during the practice of this invention, such as lower alkyl ether, lower alkyl ester, amide, nitrile, halogen substituents and the like.

Illustrative of the alpha,beta-unsaturated monomers which are suitable for use in the processes of this invention there can be mentioned the following: ethyl acrylate, N,N-diethylaminoethyl acrylate, cyanoethyl acrylate, decyl acrylate, acrylonitrile, acrylamide, dimethylacrylamide, methyl methacrylate, 2-ethylhexyl methacrylate, butyl alpha-chloroacrylate and the like. In addition, mixtures of the above monomers can also be employed.

The catalysts contemplated by this invention are the divalent alkaline earth metal amide catalysts, the metal portion of which has an atomic number of at least 4, preferably at least 12, and not more than 56, and is found in group 11A of the periodic chart of the elements as illustrated in the Handbook of Chemistry, 8th edition 1952, page 56, published by the Handbook Publishing Co., Sandusky, Ohio. More particularly, these alkaline earth metal amide catalysts can be represented by the general formula wherein M is beryllium, magnesium, calcium, barium or wherein M can be calcium, strontium, barium, and the like. The alkaline earth metal amides can then be obtained by allowing the corresponding metal hexammoniate to decompose while protecting them from reactive gases and/ or vapors such as oxygen, water, and the like. The amides of beryllium and magnesium can also be prepared for example by the reaction of diethylberyllium or diethylmagnesium with ammonia. In addition, the articles of Bergstrom and Fernelium also disclose various methods for preparing these metal amides.

The catalytic activity of the alkaline earth metal amides is quickly destroyed upon exposure to air. The preparation and storage of the catalyst should be conducted 1 Chem. Revs, 12, 43 (1933) Chem. Revs, 20, 4.13 (1937).

3 operations can be desirably carried out by suspending the catalyst in an inert liquid such as the inert organic diluents herein described.

The concentration of the alkaline earth metal amide about 150 0., thermal polymerization rather than catalyzed polymerization appears to be the predominant reaction.

The polymerization reaction can be carried out, for

or above the broad temperature range described above can also be employed. However, the rate of polymerization rapidly decreases below about 20 C., while at temperatures above about 120 to be employed as a catalyst in accordance with this in- 5 example, by adding a suspension of the catalyst in an vention can vary over a broad range. In general, a catainert organic diluent to the bulk monomeric reactant(s) lyst concentration in the range of from about 0.02 percent or to a solution or suspension of the monomeric reto about percent by weight, based upon the weight actant(s) in an inert organic diluent at the desired polyof total monomeric feed, is preferred. However, higher merization temperature, and allowing the mixture to or lower catalytically significant quantities of the alkaline 10 stand until the polymerization is completed. An alterearth metal amide can also be employed, such quantities native procedure is to add the monomeric reactant(s) to being readily determinable by those skilled in the art in a suspension of the catalyst in an inert organic diluent at light of this disclosure. For optimum results, the parthe desired polymerization temperature and at the same ticular catalyst employed, its preparation, its surface area, rate that it is being polymerized. the nature of the monomeric reactant(s), the tempera- In general, the reaction time will vary depending upon ture at which the polymerization reaction is conducted, the operating temperature, the nature of the monomeric and other factors will largely determine the desired reactant(s) employed, the particular catalyst employed, catalyst concentration. For instance, with the very finely the inert organic diluent employed, the concentration anddivided active catalysts, catalyst concentrations in the surface area of the catalyst and the like. The reaction range of from 0.02 to 0.1 percent by Weight of the monotime can be as short as minutes in duration or it can bemeric feed may be employed, accompanied by a high as long as several days. degree of catalytic efiiciency. Upon completion of the polymerization reaction, the The preferred inert organic diluents for use in this innormally solid polymeric products of this invention can vention are those which are solvents for the monomeric be recovered by filtration, or by precipitation with a nonreactant(s). It is to be noted, however, that this invensolvent followed by filtration, and are then generally tion is also applicable to suspensions of the monomeric washed with acidified methanol and dried. Other rereactant(s) in an inert organic diluent. The diluent can covery techniques will occur to those skilled in the art also be a solvent for the polymer produced although this and can also be employed in accordance with this inveni not necessary. Among the suitable inert organic tion. The following examples further serve to illustrate diluents there may be mentioned for example, the aromatthe invention. ic hydrocarbons, such as benzene, toluene, xylene, ethyl- EXAMPLE I 3 5 2 i f g are A solution of 20 grams of methyl methacrylate in 230 6 5a mate 1P 3 an eye 0a y meal 9 milliliters of hexane was placed in a dry bottle and purged such as n-hexane, octane, cyclohexane and the like. 3 with nitrogen A suspension of L0 gram of Calcium Ahphiltlcdind i f canhalso be usgd i tilefmert 5 amide in 20 milliliters of heptane was added,'and the gf g a g of E "i f bottle was capped. The bottle was rotated end over end y e 1 9 tetra y in a water bath at a temperature of 50 C. for a period 21 ggg g g i' g f bcombmlatlogs :Z of 18 hours. The solid polymer product thereby formed natively the polymerizasitiil ieitjiion c i b jarried rit 40 Was-removed by filtratlon and washed with methaliol co-nin theagsence o a diluent taming about 2 percent concentrated hydrochloric acid. The monomeric d dil nt) ould b After additionabwaslnng with methanol, the polymer free of substances which destro the catal tic eifect of product was dried In thls manger one gram of the catalyst as for example sri ch impurities as water pohgmethyl methacrylaie) WaS-Obtamed The polymer oxygen, carbon monoxide, alcohols and the like. Thus, pro uct had a reducvd vlscoslty m benzene of the polymerizations are generally carried out in dry EXAMPLE II q p using anhydrous monomeric reactant(s) and Using the procedure described in Example I for chargunder an inert gas atmosphere, such as a atm p ing the polymerization bottles and recovering the polyof helium, argon, methane, nitrogen and the like. mer product, a series of experiments illustrating the use The polymerization reaction can be carried out over a of various monomers and solvents was carried out. Op- Wrde temperature range. Depending upon various faC- crating conditions and the resulting data obtained from tors, such as the nature of the monomeric reactant(s) this series of experiments is tabulated below in Table A. employed, the particular catalyst employed, the inert or- In all of the experiments, 2 grams of calcium amide was ganrc diluent employed, the concentration and surface used as catalyst. In run nos. 1 to 3, the reduced viscosity area of the catalyst and the like, the reaction temperature 53 of the polymer product was obtained from a benzene can be as low as about 20 C. and as high as about solution; in run No. 4, a dimethylformamide solution of +l50 C. A preferred temperature range is from about the polymer product was used for this purpose.

Table A Monomer Diluent Reaction 7 Run Percent Reduced No. Yield Viscosity Name Amount Name Amount Temp. Time (Grams) (Milliliters) 0.), (Hours) mgilzleyl methacry- 30 tetrahydroiuram 150 50 18 33 1.67 Itiiiiiiiiiiiiii: 38 iiiiiiffifjjj: iii) 29 ii 133 3:32 I acrylonitrile 25 do 200 50 17 16 0.96

0 C. to 120 C. Reaction temperatures somewhat below EXAMPLE III Using the procedure described in Example I, a bottle was charged with 200 milliliters of hexane, 25 grams of acrylonitrile and 2 grams of strontium amide. The poly- C., and particularly above merization was carried out at a temperature of 50 C. for

a period of 17 hours, whereupon one gram of poly(acry1- onitrile) was recovered as a product. The polymer product had a reduced viscosity in dimethylformamide of 0.3 6.

EXAMPLE IV To 30 grams of acrylonitrile, contained in a polymeri- I Thirty milliliters (volumetric measure at a temperature of 25 C.) of methyl methacrylate was placed in a polymer-ization tube and cooled under a nitrogen atmosphere maintained at a temperature below -30 C. A suspension of 0.25 gram of calcium amide in 5 milliliters of heptane was added thereto and the tube was capped. The tube was rocked in a bath at a temperature of -8 C., for a period of two hours. The polymer product obtained in this manner was recovered and purified as de scribed in Example I, whereupon 23 grams of poly(methyl methacrylate) was obtained. The polymer product had a reduced viscosity in benzene of 2.8 6.

EXAMPLE VI A mixture of 100 milliliters (volumetric measure at a temperature of 25 C.) of toluene, 30 grams of methyl methacrylate and 2 grams of calcium amide was placed in a dry 500 milliliter flask fitted with a stirrer and reflux condenser. The mixture was stirred at reflux at a temperature of 110 C. and under a nitrogen atomsphere for a period of four hours. The polymer product obtained in this manner was recovered and purified as described in Example I, whereupon 4 grams of poly (methyl methacrylate) was obtained. The polymer prodnot had a reduced viscosity in benzene of 2.20.

What is claimed is:

l. A process for polymerizing an alpha,beta-unsaturated monomer represented by the general formula:

A CH C wherein A designates a member of the class consisting of hydrogen and halogen atoms and the alkyl radicals containing from 1 to 4 carbon atoms, and B designates a member of the class consisting of the -CN,

0 0 t OR ii NH Ii aand- -NRr radicals wherein R designates an alkyl radical containing from 1 to 4 carbon atoms, which process comprises contacting said monomer at a temperature of from about -20 C. to about C., in the presence of an inert organic diluent, with a catalytic amount, sufficient to catalyze said polymerization, of an inorganic alkaline earth metal amide of the formula H N--MNH wherein M is an alkaline earth metal atom having an atomic number of from 4 to 56, for a period of time sufficient to polymerize the monomer.

.2. A process for the polymerization of acrylonitrile which comprises contacting acrylonitrile at a temperature of from about 20 C. to about 150 C. in the presence of an inert organic diluent, with a catalytic amount, sufficient to catalyze said polymerization, of an inorganic alkaline earth metal amide of the formula H; NM-NH wherein M is an alkaline earth metal atom having an atomic number of from 4 to 56, for a period of time sufficient to produce po1y(acrylonitrile).

3. The process of claim 2. wherein said alkaline earth metal amide is calcium amide.

4. The process of claim 2 wherein said alkaline earth metal amide is strontium amide.

5. The process of claim 2 wherein said alkaline earth metal amide is magnesium amide.

6. A process for the polymerization of methyl methacrylate which comprises contacting methyl methacrylate at a temperature of from about -20 C. to about 150 C. in the presence of an inert organic diluent, with a catalytic amount, suificient to catalyze said polymerization of an inorganic alkaline earth metal amide of the formula H N-MNH wherein M is an alkaline earth metal atom having an atomic number of from 4 to 56, for a. period of time sufficient to produce poly(methyl methacrylate) 7. The process of claim 6 wherein said alkaline earth metal amide is calcium amide.

8. The process of claim 6 wherein said alkaline earth References Cited in the file of this patent UNITED STATES PATENTS 2,608,555 Bullitt Aug. 26, 1952 

1. A PROCESS FOR POLYMERIZING AN ALPHA, BETA-UNSATURATED MONOMER REPRESENTED BY THE GENERAL FORMULA: 